The primary objective of this application is to purchase an in vivo microcomputed tomography (in vivo microCT) instrument. This instrument permits the three-dimensional visualization of tissue structure at high-resolution (16 micron) in living rodents. Furthermore, the digital data permits highly quantitative determination of a variety of structural parameters. Although used most frequently for analysis of the bony skeleton, microCT can also be used to visualize a variety of other normal and pathological tissues, including cartilage, muscle, fat, vasculature, and tumor. The microCT instrument will be located in the University of Pennsylvania Small Animal Imaging Facility (SAIF) which has an integrated system for longitudinal evaluation of mice and rats using a wide-variety of imaging modalities. High-resolution microCT will represent a significant improvement on the available imaging services and will complement the light-based, fluorescence, ultrasound, and nuclear imaging technologies that already exist in the SAIF. An entire mouse, or part of a rat can be scanned under anesthesia and then the animal recovered, and the same site scanned days, weeks, or months later. Indeed this eliminates the confounding inter-animal variation in longitudinal studies, and importantly, changes with age or treatment in a single animal can be studied. Scanning live animals, repeatedly, in a longitudinal manner is more scientifically robust, and reduces the number of animals needed for any given study. This saves grant dollars, as well the reduction in the number of animals used in a study is good practice for animal welfare. The instrument will be administered by a committee of faculty members drawn from the Engineering, Dental, Medical, and Veterinary Schools at Penn. Similarly, the user group is drawn from these four Schools and also includes users from two other Philadelphia-based institutions, Children's Hospital of Philadelphia (CHOP) and Temple University. [unreadable] [unreadable] High resolution imaging of live rodents is crucial for being able to properly follow the course of experimental disease and aging in a wide-variety of animal models. Information gained from studying rodent musculoskeletal, cancer, and metabolic diseases will have direct translational application to better understanding similar disease states in humans. [unreadable] [unreadable] [unreadable]